of the high energy nucleation centers are unknown. One knows, however, that the average number of H2O molecules in a particulate should be close to the reciprocal of the fractional concentration of the nucleation center population present prior to nucleation. S^nce the fraction of nucleation center population could be as high as 10 in the non-equilibrium expansion process on hand, ^the average number of H2O molecules in an ice particle could be as low as 10H. The diameter of the particles could then be as small as 8 x 10~ cm. The above reasoning leads one to estimate tlj^t the typical sizes of the ice crystals formed should be between 10 and 10 cm. Due to electrostatic interaction among the ice crystals, however, the particulates may coagulate into larger particles. Coagulation phenomenon is observed commonly in a laboratory experiment with solid suspensions, but there is no theory to describe the phenomenon. Hence, the final sizes of the ice crystals deposited into the ambient vacuum are presently unknown. C. Orbital Mechanics of Effluents from POTV (see Figure 5). A POTV mission required five engine burns. They are named here for convenience Burns 1 through 5: Burn 1, the acceleration burn at LEO using the first stage engines to deorbit from the LEO; Burn 2, the acceleration burn at LEO using the second stage engines to circularize at the GEO; Burn 3, the deceleration burn at the GEO using the second stage engines to deorbit from the GEO; Burn 4, the deceleration burn at the LEO using the second stage engines to circularize at the LEO; and Burn 5, the deceleration burn at the LEO of the first stage vehicle using the first stage engines for circularization at the LEO. In time sequence, the Burn 5 occurs prior to Burn 3. The masses of the fuel burned, the absolute velocities of effluents, and the eventual fates of the effluents are listed in Table 8 (see also Fig. 5). In the table, the negative sign denotes the direction opposite to the earth's rotation. The finite range in the velocities given are due to the fact that the vehicles change velocity during burns. The fates of the effluents are judged simply by comparing the absolute velocities with the escape velocities, which are 10.76 km/sec at the LEO and 4.34 km/sec at the GEO. As indicated in the table, the effluents of Burn 2 are trapped in an earthbound orbit. The center of gravity of the effluent mass has a perigee of 14,400 km above sea level, an apogee of 35,800 km above sea level (GEO), and a period of 18 hours. But the effluents are spread over a wide range: some particles have a perigee as high as 30,000 km while others have one of only 3000 km. The effluents from Burns 4 and 5 will escape provided the effluents are in the condensed phase. If they are in a gaseous state, molecular collisions will slow them down and prevent escape. In the case of their being slowed down, their fate will be dictated by the velocity of the ambient molecules. One cannot assume that the ambient molecules are at rest: the construction of the SPS will inject a large momentum in the direction of the earth's rotation, so it is likely that the ambient mass will be moving in the same direction. In the imaginary donut-shaped ring around the earth, 1000-km wide and 100-km thick at around 500-km altitude wherein a large amount of rocket effluents will be deposited, the total mass of the ambient atmosphere is only of the order of 10,000 tons. The amount of matter the space activity will inject in a year far exceeds this value. However, the average velocity of the matter (including HLLV) injected into the LEO is slightly under the circular orbital
RkJQdWJsaXNoZXIy MTU5NjU0Mg==